The present invention relates in general manner to the field of solar energy generator panels, in particular for space applications. More particularly, it relates to a solar generator panel comprising an array of strings of photovoltaic cells disposed side by side and forming a substantially rectangular grid.
The solar generator panels transported in a space vehicle such as a satellite generally comprise:                an array of solar cells formed by strings of cells electrically connected to the satellite, the array covering the surface of support panels and serving to transform solar energy into electrical energy; and        said support panels supporting the arrays of cells comprising a substrate.        
Such solar generator panels can be distributed in a wide variety of configurations. Conventionally, they comprise a longitudinal succession extending parallel to a direction going away from the body of the space vehicle, and around which the generator panel is designed to turn in order to track the sun. Nevertheless, in order to increase the available electrical power, proposals have been made to deploy not only the above panels, but also additional lateral panels. Configurations are also known in which the panels are disposed in a transverse direction, i.e. in a direction extending transversely to the above-mentioned longitudinal direction along which the yoke extends that connects the generator to the body of the satellite, and about which the generator is adapted to turn in order to track the sun.
Another factor for increasing the electrical power available from panels lies in the occupancy ratio of solar cells over the panel. It is common practice to use silicon cells which enable an occupancy ratio of up to 0.94 to be achieved, which is deemed to be excellent. Naturally, this excellent result comes from the small number of strings per panel, which is a characteristic of strings of silicon cells, leading to only a small area being lost.
Nevertheless, the present trend is more and more towards the use of GaAs cells since they provide high energy conversion efficiency.
Nevertheless, several drawbacks arise when it comes to using GaAs cells:                firstly, it is necessary to find a solution to connecting the positive and negative terminals of the strings of cells, which solution must be capable of optimizing the space occupied by the terminals;        secondly, it is known that if the voltage between adjacent cells is above a certain threshold, then the working current from the string can flow between two cells via a plasma created by a primary electrostatic discharge. This secondary arc sustained by the working current of the generator can be maintained for several seconds or more. It is then found that the secondary arc dissipates sufficient energy to heat the insulating substrate, up to a temperature where the high resistance polymer becomes transformed into a material having very low resistance. This process of pyrolysis leads to a permanent short circuit between the two cells, and thus between two rows of adjacent cells, which leads to permanent destruction of a portion of the solar generator, which then becomes incapable of delivering all of its working power to the equipment of the satellite.        
For panels in which the + and − terminals of the strings of cells are on the same edge of the panel, usually referred to as being a U-shaped configuration, two + and − terminals which are associated with the same U-shape are relatively close together and at a potential difference equal to the total voltage drop along the corresponding string. Thus, the maximum potential difference appears between these successive terminals and between two contiguous cells which are each respective ends of the same U-shaped string. As a result of the small distance between the cells (or the terminals) associated with a high potential difference, there is a risk of an electric arc appearing, as explained above.
That is why it is necessary to set a maximum voltage between adjacent cells (of about 40 volts (V)).
Furthermore, a method of reducing the risks of secondary discharge between adjacent rows lies in increasing the spacing between rows of cells. Nevertheless, the spacing created in this way leads to a reduction in the cell occupancy ratio of the panel, thereby decreasing the solar energy power that the panel can collect. In the present state of knowledge, the occupancy ratio of GaAs cells reaches a maximum in the range 0.90 to 0.92.This ratio is achieved in particular by using cells obtained by the method as shown in FIG. 1 whereby cells 1 are cut from disks 2 of germanium (Ge), where said disks are commonly referred to as “wafers”, which means that corners are cropped between adjacent cells 1. The supply of the cells 1 have taken the habit of cutting the square 3 into two in order to provide two rectangular cells each having two chamfered corners, both cells being taken from the same disk 2.
FIG. 2 shows strings 4 of cells of the kind that have been used until now. The string 4 is constituted by solar cells 1 connected in pairs in series, thus forming a row of cells. The ends of the string 4, which can be located on the same row or on different rows, are each connected to a + or − terminal of the panel so that the electric current delivered by each string is collected by wiring 5 and taken, via dedicated openings 6 and cabling installed on the rear face, to the equipment of the satellite. However, the area 7 dedicated to the cables 5, to their connections to the end cells, and to the connection opening generally corresponds to the area occupied by one cell, or even more, thereby considerably decreasing the occupancy ratio of the panel.